Functional Imaging of Neurocognition

Mark D'Esposito, M.D., Helen Wills Neuroscience Institute and Department of Psychology, University of California, Berkeley, California.

Semin Neurol. 2000;20(4) 

In This Article

Abstract and Introduction

Neuroimaging has, in many respects, revolutionized the study of behavioral neurology and cognitive neuroscience. Early studies of brain-behavior relationships relied on a precise neurological examination as the basis for hypothesizing the site of brain damage that was responsible for a given behavioral syndrome. The advent of structural brain imaging, first with computed tomography (CT) and later with magnetic resonance imaging (MRI), paved the way for more precise anatomical localization of the cognitive deficits that are manifest after brain injury. In recent years, functional neuroimaging, broadly defined as techniques that provide measures of brain activity, has further increased our ability to study the neural basis of behavior. The modern era of functional brain imaging was introduced with the use of positron emission tomography (PET). In more recent years, functional magnetic resonance imaging (fMRI) has rapidly emerged as an extremely powerful technique with many advantages over PET for studying cognition. Thus, the principles underlying fMRI studies of cognition are the focus of this review.

Neuroimaging has, in many respects, revolutionized the study of behavioral neurology and cognitive neuroscience. Early studies of brain-behavior relationships relied on a precise neurological examination as the basis for hypothesizing the site of brain damage that was responsible for a given behavioral syndrome. For example, nonfluent aphasia, usually associated with right hemiparesis, clearly implicated the left hemisphere as the site of language abilities. Clinicopathological correlations were the earliest means of obtaining precise data on the site of damage causing a specific neurobehavioral syndrome. In 1861, Paul Broca's observations of nonfluent aphasia in the setting of left inferior frontal gyrus damage cemented the belief that this brain region was critical for speech output.[1] The advent of structural brain imaging more than 100 years after Broca's observations, first with computed tomography (CT) and later with magnetic resonance imaging (MRI), paved the way for more precise anatomical localization of the cognitive deficits that are manifest after brain injury. Anatomical analyses of Broca's aphasia using structural neuroimaging[2,3,4] have more precisely determined that damage restricted to the inferior frontal gyrus causes only a transient aphasia, with recovery within weeks to months. Instead, damage to deep white matter and insular cortex causes persistent nonfluency. Noninvasive, structural neuroimaging provides the remarkable power to detail anatomical pathology in every stroke patient without re-lying upon the infrequently obtained autopsy.

Functional neuroimaging, broadly defined as techniques that provide measures of brain activity, has further increased our ability to study the neural basis of behavior. Functional neuroimaging dates back to the use of electrophysiological methods such as electroencephalography (EEG). However, the lack of spatial resolution in these methods (i.e., often limited to hemispheric or anterior-posterior differences) did not allow testing hypotheses regarding the precise anatomical location of a brain region subserving a given cognitive process.[5] The modern era of functional brain imaging, bringing markedly improved spatial resolution, was introduced first in the mid-1970s using the xenon cerebral blood flow technique6 and later in the mid-1980s using positron emission tomography.[7,8] In more recent years, functional magnetic resonance imaging (fMRI) has rapidly emerged as an extremely powerful technique with many advantages over positron emission tomography (PET) for studying cognition. Thus, the principles underlying fMRI studies of cognition are the focus of this review.

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